Find it by sine theorem? Size? VB=ve.sin30 degrees /sin( 180 degrees -(θ+30 degrees) =v/(2sin( 180 degrees -(θ+30 degrees)).

ωOB=vB/OB

Acceleration vector equation? aB=aBt+aBn=ar+ae？ ? (2)

Size: aBt, ar unknown; abn=ob.ωob^2； ae=a .

(2) The projection of the formula to aBt direction? ABt=ae.cosθ-ar.sin( 180 degrees -( 120 degrees +θ)) (3)

(2) The projection of the formula to aBn direction? ABn=-ae.sinθ+ar.cos( 180 degrees -( 120 degrees+θ))? (4)

(3) Formula (4) can be solved simultaneously:? aBt、ar

εOB=aBt/OB

* Solve the equation and substitute the original data.